Indicating instruments provided with a movable iron strip member

ABSTRACT

In a moving iron-type instrument including a movable vane and a fixed vane which are magnetized by the magnetic flux created by an exciting coil energized by an electric quantity to be measured to rotate the movable vane by a magnetic repulsive or attractive force acting between the rotary and fixed vanes, there are provided a flat plate-shaped movable vane located outside of the exciting flat plate-shaped fixed vane located between the movable vane and the exciting coil to be parallel with a plane described by the rotary movement of the movable vane.

United States Patent Inventors Hidekazu Okada Kunitachi-shi, Tokyo;Takahiko Aoki, Tokyo; Ryozi Narita, Tokyo, all of, Japan Appl. No.704,940

Filed Feb. 12, 1968 Patented June 15, 1971 Assignee Tokyo ShibauraElectric Co., Ltd. Kawasaki-shi, Japan Priority Feb. 16, 1967, Feb. 3,1968, Feb. 3, 1968,

Feb. 3, 1968 Japan INDICATING INSTRUMENTS PROVIDED WITH A MOVABLE IRONSTRIP MEMBER 6 Claims, 25 Drawing Figs.

US. Cl 324/147, 324/132 Int. Cl G011 1/20 Field of Search 324/ 147,

I 56] References Cited UNITED STATES PATENTS 393,088 11/1888 Waterhouse324/147 2.610.988 9/1952 Wiese 324/147 FOREIGN PATENTS 221,035 3/1909Germany i I 324/147 1,033,777 7/1958 Germany 324/147 142,900 5/1920England 324/147 Primary Examiner-Alfred E. Smith Attorney-George B.Oujevolk 5 7 g he 7 FIGJ V BY c e/t5 OVUWWW PATENTEU JUN] 51% 3; 585;501

sum 2 OF 4 INDICATING INSTRUMENTS PROVIDED WITH A MOVABLE IRON STRIPMEMBER This invention relates to a moving iron-type instrument and moreparticularly to a moving iron-type instrument suitable for providingindications on a wide range scale.

As is well known in the art, the moving iron-type instrument comprisesan exciting coil energized by an electric quantity such as current of ameasured circuit. A movable shaft extending through the center of thecoil, a fixed vane and a movable vane is so arranged as to form portionsof a cylindrical surface concentric with the inner wall of the coil.Upon magnetization of the movable and fixed vanes by the exciting coil,a repulsive or attractive force is created between these vanes to causethem to repel and attract each other thus rotating the movable shaftwhich supports the movable vane.

Inasmuch as the instrument of this type responds to the first power ofthe voltage or current of an alternating current or direct current it isdesirable that the relation between the current flowing through theexciting coil and the angle of deflection of the movable shaft orpointer should be linear. However, as the repulsive force or attractiveforce created in this type of instrument is proportional to the squareof current it is not possible to establish the desired linearrelationship between current and torque unless the configuration of thestationary vane secured to the spool of the exciting coil is designed tohave a complicated shape.

While the operation of such an instrument is satisfactory for a scalecovering 90, for wider range scales covering 240- 270, by the reasonsenumerated below it is necessary to rely upon very troublesome measuresto shape and work component parts, to securely fix the fixed and movablevanes, and to correct and adjust completed parts.

I. As the fixed vane for creating the repulsive force or attractiveforce is opposed to the movable vane which rotates about the movableshaft, it is necessary to form the fixed vane to have an exactcylindrical form concentric with the cylindrical surface described bythe rotary movement of the movable vane.

2. Usually, the fixed vane is formed as a flat piece by stamping andthen bent into the desired configuration such as cylindrical and thelike configuration. However, it is very difficult to accurately bend theflat piece into the required configuration.

3. Further, it is necessary to arrange and secure the fixed and movablevanes in correct relative positions both in the longitudinal andtransverse directions of the movable shaft.

Accordingly, one of the objects of this invention is to provide a movingiron-type instrument in which precision working and assembly of themovable vane as well as the stationary vane are easy.

Another object of this invention is to provide an improved movingiron-type instrument having a substantially uniform scale over a widerange, i.e. the spacing between scales for large deflection angles issubstantially equal to that for moderate deflection angles.

These and other objects can be attained according to this invention byproviding a moving iron-type instrument comprising an excitingcoiladapted to be excited by the electric quantity to be measured, a movablevane arranged outside said exciting coil to be rotatable about the axisof said coil, and to be magnetized by said coil when it is energized,and a flat platetype fixed vane having a required contour, said fixedvane being positioned outside said coil and between said coil and saidmovable vane in substantially parallel relationship with a planedescribed by the rotary movement of saidmovable vane to be magnetized bysaid coil when it is energized.

Upon energization of the coil by the measured electric quantity bothmovable vane and flat plate-shaped fixed vane are magnetized to anintensity corresponding to said measured quantity wherebyto create arepulsive or attractive force between these vanes to rotate the movablevane. Accordingly,

a pointer mounted on the movable vane measures such electric quantitiesas voltage, current or power. The contour of the movable vane may be anelongated plate while that of the fixed vane may be a plate with anouter periphery gradually decreasing or increasing as hereinafterdescribed in radius in the direction of rotation of the movable vane. Asa result these vanes can be manufactured readily. Further, as thesevanes are disposed outside the exciting coil they'can be assembledreadily and accurately.

Further, as the change in the angle of rotation of the moving vane isdetermined dependent upon theperipheral contour of the fixed vane it ispossible to provide the desired wide range scale for the instrument bythe proper selection of the peripheral contour of the fixed vane.

The foregoing objects and other objects as well as characteristicfeatures of the invention will become more apparent and more readilyunderstandable from the following description and the appended claimswhen read in conjunction with the accompanying drawings in which:

FIG. 1 shows a longitudinal section of a moving iron-type instrumentembodying this invention;

FIG. 2 shows an enlarged longitudinal section of essential portions ofthe instrument shown in FIG. 1;

FIG. 3a shows a front view of the essential portions shown in FIG. 2;

FIG. 3b shows a front view of modified essential portions from thoseshown in FIG. 3a;

FIG. 4 shows a front view of modified essential portions from thoseshown in FIG. 3a;

FIG. 5 shows a front view of a scale board utilized in the instrumentshown in FIGS. 1 to Sat;

FIG. 6 is a front view illustrating another example of the essentialportions shown in FIG. 3a;

FIG. 7 is a front view to aid the understanding of the essentialportions shown in FIG. 6;

FIGS. 8 and 9 show still further modifications of the essential portionsshown in FIG. 4a;

FIG. 10 is a side view of the embodiment shown in FIG. 9 as viewed inthe direction of an arrow;

FIGS. 11 and 12 illustrate perspective views of the movable vanes ofdifferent type;

FIG. 13 is a longitudinal sectional view of another embodiment of thisinvention;

FIGS. 14 through 18 show longitudinal sections of differentmodifications of the essential portions shown in FIG. 13;

FIG. 19 is a longitudinal sectional view of yet another embodiment ofthis invention;

FIGS. 20 and 21 show longitudinal sections of modifications of theessential portions shown in FIG. 19;

FIG. 22 is a longitudinal sectional view of a different embodiment ofthis invention including a pair of movable vanes and a pair of fixedvanes; and

FIGS. 23 and 24 are longitudinal sectional views illustratingmodifications of the essential portions shown in FIG. 22.

Referring now to FIG. 1 of the accompanying drawings, the instrumentshown therein includes a movable shaft 1 with its opposite endsjournaled by bearings 2 and 3. A pointer 4 and a control spring 5 aresecured to movable shaft 1. Further a movable vane 6 of soft iron isfixed to the movable shaft 1 in perpendicular to the axis thereof. Themovable vane 6 is disposed outside an exciting coil 7 with said movableshaft extending through its center. The exciting coil 7 is supported bya frame 8 to which bearings 2 and 3 are secured. The frame 8 alsosupports a flat plate-shaped soft iron stationary vane 9 disposedbetween movable vane 6 and the exciting coil 7.

In the central portion of the fixed vane 9 there is provided a circularhole 9: of a suitable diameter for inserting the movable shafttherethrough. The periphery 9a of the fixed vane 9 is formed such thatthe radius thereof gradually decreases in the direction of the rotationof the movable vane 61 (in the direction shown by an arrow) or graduallyincreases in the direction of the rotation of the movable vane 62 (inthe same direction as that of the movable vane 61 as shown in FIG. 3a)

as shown in FIG. 3b. As evident from FIGS. 3a and 3b, the fixed vane 9having such a periphery as to gradually decrease in diameter in thedirection of the rotation of the movable vane 61 or 62 and the fixedvane 9 having such a periphery as to gradually increase in diameter inthe direction of the rotation thereof are entirely same in configurationto each other and can be used by selectively turning up the top orbottom side of the fixed vane as required. When the fixed vane 9 is usedin such a position that the radius of the fixed vane gradually decreasesin the direction of the rotation of the movable vane 61 as shown in FIG.30, use is made of such a movable vane that the starting end of themovable vane is selected as positioning near the maximum outer diameterportion of the fixed vane 9 and that the outer end 61a fixed at itsinner end 61b to the movable shaft 1 substantially corresponds to themaximum outer diameter portion ofthe fixed vane 9.

Alternatively, when the fixed vane is used in such a position that theradius thereof gradually increases in the direction of the rotation ofthe movable vane 62, use can be made of such a movable vane that thestarting end thereof is selected as positioning near the minimum outerdiameter portion of the fixed vane and that the outer end 62a fixed atits inner end 62b to the movable shaft 1 substantially corresponds tothe minimum outer diameter portion of the fixed vane. Therefore,energization of the exciting coil 7 will create a magnetic field betweenthe fixed vane and the movable vane, causing the periphery 9a of thefixed vane 9 to be magnetized to either N or S pole.

Thus, if it is assumed now that the exciting coil 7 is energized bydirect current or alternating current to produce magnetic flux around itin the direction shown by dotted line arrows in FIG. 2, the fixed vane 9will be magnetized such that its outer periphery 90 becomes an N polewhile its inner periphery 9b becomes an S pole. In the same manner, themovable vane 61 (62) will be magnetized to form an N pole at its outerend 61a (620) an S pole at its inner end 61b (or 62b). Thus, a repulsiveforce will be created between the outer end 61a (62a) of the movablevane and outer periphery 9a of the fixed vane which are magnetized tothe same polarity to rotate the movable vane 61 (62) in the clockwisedirection to a point where the repulsive force and the resiliency of thecontrol spring 5 balance each other.

The reason that the movable vane 61 (62) is driven in the clockwisedirection can be explained as follows: As shown in FIG. 3a or FIG. 3b,the rotation locus 10 of the outer end 61a (62a) of the movable vane 61(62) is a true circle about the shaft 1, whereas as the radius of theouter periphery 9a of the fixed vane gradually decreases (or increases)in the clockwise direction, the radial distance d, between the outer end61a (or 62a) of the movable vane and the outer periphery 9a of the fixedvane increases gradually as the movable vane rotates in the clockwisedirection. As this distance d increases, the repulsive force between theouter end 61a (62a) and the outer periphery 9a will decrease inverselyproportional to the square of distance Thus it will be seen that bymagnetizing the outer end 61a (62a) and the outer periphery 9a to thesame polarity the movable vane 61 (62) will be driven in a direction inwhich the repulsion between the outer end 61a (62a) and outer periphery9a decreases, or in the clockwise direction as viewed in FIG. 3a (orFIG. 3b). This relation can be expressed by mathematic equations asfollows:

To obtain an uniform scale instrument over the full range of rotation ofthe movable vane 61 or 62, it is only required that there always beestablished the relationship expressed by the following equation:

iaKo X 0 Substituting the above eq ua tIonYB') in the equation (4),there will result 01: K0\ 0 (6) Where: M

Ka of equations (5) and (6) is a constant. It, therefore, the outerperiphery 9a of the fixed vane 9 is so chosen as to satisfy therelationship represented by the equation (6), then it will be apparentthat there will be obtained a uniform scale instrument over the fullrange of rotation of the movable vane 61 or 62.

Expressed in terms of the radius r of the fixed vane 9, the relationshipof the equation (6) above will run as follows:

In case of FIG. 3a FAN-KM In case of FIG. 3b r=r +KM Where:

r or r radius of that part of the fixed vane 9 which faces the zero orrest position of the movable vane 61 or 62 when the coil 7 isdeenergized. In case of FIG. 30 it represents a substantially maximumradius of the fixed vane 61 and in case of FIG. 3b a substantiallyminimum radius of the fixed vane 62.

K constant.

To obtain the aforesaid uniform scale instrument, therefore, it is onlyrequired to define the outer periphery 9a of the fixed vane 9 so as tosatisfy the relationship of the equation (7) or (8).

The foregoing is simply a theoretical discussion. In practice,therefore, necessary corrections should be made.

Further, where a magnetic body 20 of soft iron as shown by a dotted linein FIG. 5 is positioned near the portions of large deflection angles 11aof the scale board 11, the magnetic body 20 will be magnetized to apolarity opposite to that of the outer end 61a of the movable vane whenthe exciting coil 7 is energized, whereby the movable vane 61 will beattracted against the repulsive force between said side 61c anddiscontinuous surface 9e, thus further increasing the scale spacings atthe portion of large deflection angles 11a of the scale board 11. Saidmagnetic body 20 is formed threadable so that its level of height may beadjusted to control the intensity of said attractive force.

Further, a combination of said magnetic body 20 and the fixed vane 9 asshown by a dotted line in FIGS. 5 and 4 respectively may render thescale on the scale board 11 uniform.

As shown in FIG. 6, it is desirable to provide a suitable stop 19 atsuch a position that when the pointer 4 engages with the stop 19 theside surface 61d of the movable vane will be displaced clockwise by anangle 0;, from the discontinuous surface 9e of the fixed vane.

With this arrangement as there is always a repulsive force between theside surface 6d and the discontinuous surface 9e with the result thateven when the pointer 4 is engaging with the stop 19 the movable vane 6can rotate in the normal or clockwise direction.

As shown in FIG. 7, if the stop 19 were positioned such that the sidesurface 6d of the movable vane 6 would be displaced by an angle .9 fromthe discontinuous surface 9e of the fixed vane in the counterclockwisedirection, the movable vane 6 would be subjected to a torque in thecounterclockwise direction due to the repulsive force created betweenthe side surface 6d and the discontinuous surface 9e when the pointer 4comes to engage with the stop 19, whereby the movable vane 6 will becontinuously maintained at the position shown in FIG. 7. For this reasonit is desirable to locate the stop 19 at the position shown in FIG. 6 soas to ensure that the movable vane rotates in the desired direction whenthe instrument is energized. Such an object can also be attained byother suitable means that the provision of stop 19 as by bending thediscontinuous surface 9e in a direction other than the radial direction.

Further as shown in FIG. 8, it is desirable to shape the outer contour9a of the fixed vane 9 such that the radius r of a portion of its outerperiphery 9a facing to the movable vane 6 when the input to the excitingcoil 7 is zero decreases rapidly.

With this construction even when the input to the exciting coil 7increases rapidly the movable vane can rotate in the normal or clockwisedirection, thus preventing its reverse rotation.

Suppose now that the movable vane 6 is rotated and stopped at a point Xby a certain input applied to the exciting coil 7.

If the input were increased gradually from zero, the movable vane 6would rotate in the normal direction or in the clockwise direction andstop at the required point X. On the contrary, upon rapid increase ofthe input from zero, the movable vane 61 may rotate in the oppositedirection by the shock of said rapid increase so that the pointer comesto collide against the stopper 19 and the movable vane cannot assume thedesired position X. As reasons why such phenomenon occurs, the followingfactors will be considered. Namely, in the initial stage where the fixedand movable vanes have been magnetized by the magnetic field produced bythe exciting coil, torques for rotating the pointer 4 in the clockwisedirection or in the counterclockwise direction and produced in such adirection that the repulsive force between the outer periphery of thefixed vane and the outer end of the movable vane is gradually decreaseddue to the fact that the radial distance d between the outer peripheryof the fixed vane and the rotation locus described by the outer end of amovable vane gradually increases in the desired direction of therotation of the movable vane. However, the rotational torque caused bysuch repulsive force is not effectively acted upon with respect to theinput such as the rapid increase of the input from zero, thus causingsuch phenomenon mentioned above to take place. However, when the radiusof a portion 90 of the periphery of the fixed vane 9 is abruptlydecreased as above described, the increment of :1 becomes larger whenthe movable vane 61 rotates in the clockwise direction than when themovable vane rotates in the counterclockwise direction. Thus, themovable vane 61 rotates in the direction in which d increases rapidly orin the direction in which the repulsive force decreases rapidly(clockwise direction).

Alternatively, it is also possible to assure rotation of the movablevane 61 in the correct direction by inclining a portion 9d of the fixedvane 9 towards the movable vane 61 near the stop 19, as shown in FIGS. 9and 10.

It is to be understood that the shape of the movable vane 61 is notlimited to'an elongated strip as shown in the above describedembodiments, but may be a sector in FIG. 11 of a rectangle 60 with anarcuate tip 6d as shown in FIG. 12.

As shown in FIG. 1, the frame 8 is supported on a base 13 through posts12, which, in turn, is supported by a casing 14. The casing 14 has acylindrical form with a glass cover 15 on its front end.

In FIG. 1, as the frame 8 is bulky and as the shaft I is extendingthrough the center of the coil bobbin 18, the construction is relativelycomplicated and difficult to assemble precisely.

To avoid this difficulty, as shown in FIG. 13, it is advantageous toreduce the length of the shaft 1 so as to support the opposite ends ofthe shaft by bearings 2 and 3 in the frame 8 positioned outside the coilbobbin 18, said frame 8 being secured to base 13 through posts 12 and asupporting plate 251. Other portionsin FIG. 13 are designated by thesame reference numerals as in FIG. 1 to avoid repetition of theirdescription.

FIGS. 14 through 18 show various modifications of this invention.

For the sake of description, modified portions along are showed in theseFIGS. While in the embodiment shown in FIG. 13, the fixed vane 9 wasshown as being interposed between the frame 8 and the supporting plate21, in the modification shown in FIG. 1d, the frame 8 is interposedbetween the fixed vane 9 and the supporting plate 21. Alternatively, asshown in FIG. 15, a central bore 18a of the bobbin 18 shown in FIG. 13may be omitted or it may be a blind hole 18b as shown in FIG. 16.Further, as shown in FIG. 17 the supporting plate 21 may be omitted toconnect the bobbin 18 and the base 13 directly or through posts 12.Alternatively, as shown in FIG. 18, a magnetic core 22 may be providedin the center of the bobbin 18 to cooperate with the fixed vane 9 or acoil casing 23 may be applied onto the outer surface of the bobbin 18 tocooperate with the core 22. By the construction shown in FIG. 18, themagnetic flux produced by the exciting coil 7 will be effectivelydirected toward the fixed vane 9.

FIGS. 19 through 21 show preferred constructions of mounting the fixedvane 9. In the arrangement shown in FIG. 19, the frame 8 is formed witha boss 80 snugly received in the central bore 9f of the fixed vane 9 toaccommodate the fixed vane 9 in a recess 8d of the frame 8, wherebycenters of the fixed vane 9, frame 8 and shaft 1 can be readily aligned.

In the arrangement shown in FIG. 20, the frame 8 is interposed betweenthe supporting plate 21 and the fixed vane 9 which is supported by aclamping plate 24. Although in FIG. 19, the supporting plate 21 issecured to the base 13 through posts 12, the coil bobbin 18 and base 13may be interconnected directly or through posts 12, without utilizingthe supporting plate 21 as shown in FIG. 21.

Although in any of the above described embodiments, only one movablevane 6 and only one fixed vane 9 were used, as shown in FIG. 22 movablevanes 6 may be secured on the opposite ends of the shaft 1 to cooperatewith independent fixed vanes 9, respectively.

With this construction the torque of the shaft 1 can be doubled.

FIGS. 23 and 24 illustrate modifications of essential portions shown inFIG. 22. In FIG. 23 a pipe 16 of soft iron is fit over the shaft 1 tomagnetically couple two movable vanes 6, thus increasing the torque ofthe shaft 1, whereas in the arrangement shown in FIG. 2d a pipe 17 ofsoft iron for magnetically interconnecting fixed vanes 9 is shown asbeing fit to the inner surface of the coil bobbin 18.

While in the foregoing description the invention has been described withreference to preferred embodiments thereof, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departure from the true spirit and scope of theinvention as recited in the appended claims.

What we claim is:

1. A moving iron-type instrument, comprising:

a. a casing; I

b. a cylindrical exciting coil secured to said casing and energized byan electrical quantity to be measured to produce a magnetic field aroundsaid coil;

c. at least one fixed flat plate vane lying in a first plane parallel tothe end of the cylinder and being substantially circular, with the coilaxis passing through the center;

d. at least one movable flat plate vane lying in a second plane parallelto the end of the cylinder outside said coil, comprising a radiallyextending member whose length is the same as at least one of the radiiof the substantially circular fixed vane, and being so disposed as tolocate said fixed vane between said movable vane and the end of saidcylinder, set in a position corresponding to the radial portion of saidfixed vane with said coil deenergized, and allowed to rotate about theaxis of said coil and in a predetermined direction, when said movableand fixed vanes are magnetized by said magnetic field produced aroundsaid coil, due to the repulsive or attractive force created between saidmovable and fixed vanes, said fixed vane having a radially changingouter periphery such that the radial distance between the outerperiphery of the fixed vane and the rotation locus defined by the outerend of said movable vane is gradually increased with respect to thepredetermined direction in which said movable vane rotates;

e. support means including a shaft to rotatably support said movablevane and a restraining control spring to permit only a controlledrotation of said shaft, holding means to support said fixed vane; and,

f. an indicating means to indicate said measured electric quantityapplied to said exciting coil by the extent of rotation of said movablevane.

2. A moving iron-type instrument according to claim 1 wherein theperipheral contour of said fixed vane is selected such that the radialdistance d between the periphery thereof and the rotation locusdescribed by the outer end of said movable vane gradually increases assaid movable vane rotates in the normal direction and that said contoursatisfies a relation den where 0 represents the angle of the rotation ofsaid fixed vane.

3. A moving irontype instrument according to claim 2 wherein at leastone magnetic piece is provided at a position where said movable vanecomes to face said fixed vane when said movable vane rotates in thenormal direction by the maximum angle.

4. A moving iron-type instrument according to claim 2 wherein theperipheral contour of said fixed vane is shaped such that the radialdistance between the periphery of said fixed vane and the outer end ofsaid movable vane is rapidly increased at the radius of a portion wheresaid movable vane faces said fixed vane when they are not magnetized.

5. A moving iron-type instrument according to claim 1 wherein only onemovable vane and only one fixed vane are provided and wherein saidmovable vane is secured to a shaft extending through the center of saidexciting coil on the one side thereof 6. A moving iron-type instrumentaccording to claim 1 wherein two movable vanes and two fixed vanes areprovided and said movable vanes are secured to a shaft extending throughthe center of said exciting coil on the opposite sides thereof.

1. A moving iron-type instrument, comprising: a. a casing; b. acylindrical exciting coil secured to said casing and energized by anelectrical quantity to be measured to produce a magnetic field aroundsaid coil; c. at least one fixed flat plate vane lying in a first planeparallel to the end of the cylinder and being substantially circular,with the coil axis passing through the center; d. at least one movableflat plate vane lying in a second plane parallel to the end of thecylinder outside said coil, comprising a radially extending member whoselength is the same as at least one of the radii of the substantiallycircular fixed vane, and being so disposed as to locate said fixed vanebetween said movable vane and the end of said cylinder, set in aposition corresponding to the radial portion of said fixed vane withsaid coil deenergized, and allowed to rotate about the axis of said coiland in a predetermined direction, when said movable and fixed vanes aremagnetized by said magnetic field produced around said coil, due to therepulsive or attractive force created between said movable and fixedvanes, said fixed vane having a radially changing outer periphery suchthat the radial distance between the outer periphery of the fixed vaneand the rotation locus defined by the outer end of said movable vane isgradually increased with respect to the predetermined direction in whichsaid movable vane rotates; e. support means including a shaft torotatably support said movable vane and a restraining control spring topermit only a controlled rotation of said shaft, holding means tosupport said fixed vane; and, f. an indicating means to indicate saidmeasured electric quantity applied to said exciting coil by the extentof rotation of said movable vane.
 2. A moving iron-type instrumentaccording to claim 1 wherein the peripheral contour of said fixed vaneis selected such that the radial distance d between the peripherythereof and the rotation locus described by the outer end of saidmovable vane gradually increases as said movable vane rotates in thenormal direction and that said contour satisfies a relation d thetawhere theta represents the angle of the rotation of said fixed vane. 3.A moving iron-type instrument according to claim 2 wherein at least onemagnetic piece is provided at a position where said movable vane comesto face said fixed vane when said movable vane rotates in the normaldirection by the maximum angle.
 4. A moving iron-type instrumentaccording to claim 2 wherein the peripheral contour of said fixed vaneis shaped such that the radial distance between the periphery of saidfixed vane and the outer end of said movable vane is rapidly increasedat the radius of a portion where said movable vane faces said fixed vanewhen they are not magnetized.
 5. A moving iron-type instrument accordingto claim 1 wherein only one movable vane and only one fixed vane areprovided and wherein said movable vane is secured to a shaft extendingthrough the center of said exciting coil on the one side thereof.
 6. Amoving iron-type instrument according to claim 1 wherein two movablevanes and two fixed vanes are provided and said movable vanes aresecured to a shaft extending through the center of said exciting coil onthe opposite sides thereof.